Monitoring in an internet protocol (IP) domain

ABSTRACT

A method of facilitating monitoring of a multimedia call made up of a plurality of component parts, to enable the multimedia call contents to be identified at a predetermined location, the multimedia call originating from a location at which a first communications protocol operates and passing through at least one location where a second communications protocol operates to a destination, the method comprising the steps of: identifying the component parts of the multimedia call; removing one or more control signals from the component parts to form a call control signal for the multimedia call and a set of remaining component parts of the multimedia call; forming a multiplexed stream of the remaining component parts of the multimedia call; independently transmitting the call control signal and the multiplexed stream to the predetermined location to enable the component parts of the multimedia call to be determined in order to identify multimedia call contents.

TECHNICAL FIELD

This invention relates to improvements in or relating to monitoring orlawful interception in an Internet protocol (IP) domain, particularlybut not exclusively in relation to multimedia calls such as, forexample, video calls.

BACKGROUND

Mobile networks are currently evolving from pure circuit switched (CS)networks towards Internet protocol (IP) based networks. This hasresulted in evolution steps equivalent to that of the wireline networksin that Voice over IP (VoIP) via digital subscriber line (DSL) or widelocal area network (WLAN) access is being realized. The mobile operatorsthat install an IP multimedia subsystem (IMS) network and offer IMSservices have a need for interworking between the CS domain and the IMSdomain. This is required for all types of traffic, including videocalls, multimedia telephony calls and the like.

There are a number of problems which exist in respect of CS-IMSinterworking of video calls. One of these is the need for monitoring(also known as legal or lawful interception) of video calls. Themonitoring will be required to be carried out in a Mobile Soft Switch(MSS), for example. However, this is not simple due to the fact thatmonitoring is not typically done in an interworking node, but instead ina node in the CS domain, the IMS domain or both. In addition, the mediagateway control function (MGCF) will be integrated into the MSS and assuch monitoring (lawful interception) will need to take this intoaccount.

Video calls in the CS domain (CS video calls) have been handled as ifthey were pure data calls. As such the video support has not been acomplex issue as the CS data channel has contained audio, video andcontrol information in a multiplexed manner. In order to interwork theCS data channel (including video) with IMS it is necessary to interworkeach of the different components of the video call in the IMS domain,namely the video, audio and control information.

SUMMARY

One object of the present invention is to provide the method andapparatus for interworking between different communication protocols fora video call, which overcomes at least some of the problems associatedwith the prior art.

Another object of the present invention is to provide a method andapparatus of monitoring video calls for lawful interception.

A still further object of the present invention is to provide a methodand apparatus for enabling monitoring on a video call which has beenderived from a specific communication protocol.

The present invention provides a method and system as described in theaccompanying claims.

In accordance with one aspect of the present invention, there isprovided a method of facilitating monitoring of a multimedia call madeup of a plurality of component parts, to enable the multimedia callcontents to be identified at a predetermined location, the multimediacall originating from a location at which a first communicationsprotocol operates and passing through at least one location where asecond communications protocol operates to a destination. The methodcomprises the steps of identifying the component parts of the multimediacall; extracting one or more control signals from the component parts toform a call control signal for the multimedia call and a set ofremaining component parts of the multimedia call; forming a multiplexedstream of the remaining component parts of the multimedia call; andindependently transmitting the call control signal and the multiplexedstream to the predetermined location to enable the component parts ofthe multimedia call to be determined in order to identify multimediacall contents.

According to a second aspect of the present invention there is provideda module for a communication network for facilitating monitoring of amultimedia call made up of a plurality of component parts, to enable themultimedia call contents to be identified at a predetermined location,the multimedia call originating from a location at which a firstcommunications protocol operates and passing through at least onelocation where a second communications protocol operates to adestination. The module comprising a signal processing module forextracting one or more control signals from the component parts to forma call control signal for the multimedia call and a set of remainingcomponent parts of the multimedia call; a multiplexed module for forminga multiplexed stream from the remaining component parts of themultimedia call; independent transmission modules for transmitting eachof the call control signal and the multiplexed stream to thepredetermined location to enable the component parts of the multimediacall to be determined in order to identify multimedia call contents.

The module may be implemented on a single network node or distributedover several network nodes.

In an embodiment of the invention the call control signals forms a firsttype of communication and may be a printout communicated to thepredetermined location as the multimedia call is set up. Also themultiplexed stream forms a second type of communication and may be asingle UDI (Unrestricted Digital Information protocol) signal.

In an embodiment of the invention the multimedia call originates from anIP multimedia subsystem (IMS) network and passes through at least onelocation where a circuit switched (CS) protocol operates.

In an embodiment of the invention the call control signal may include: amultiplexing scheme, a coding scheme, or call parameters or any otherrelevant information.

In an embodiment of the invention this may be computer implemented.

In accordance with a still further aspect of the present invention thereis provided method of monitoring, at a predetermined location, amultimedia call made up of a plurality of component parts whichplurality of components have been separated into a call control signaland a multiplexed stream made up of a multiplex of remaining componentswhich do not form part of the call control signal, the multimedia calloriginating from a location at which a first communications protocoloperates and passing through at least one location where a secondcommunications protocol operates to a destination. The method comprisesthe steps of receiving the call control signal and the multiplexedstream at the predetermined location; de-multiplexing the multiplexedstream based on a first component part in the call control signal;de-coding the remaining components based on a second component part inthe call control signal; and recombining the remaining components toenable monitoring to the original multimedia call.

A further aspect of the present invention provides a lawful interceptionmonitoring centre for monitoring a multimedia call made up of aplurality of component parts which plurality of components have beenseparated into a call control signal and a multiplexed stream made up ofa multiplex of remaining components which do not form part of the callcontrol signal, the multimedia call originating from a location at whicha first communications protocol operates and passing through at leastone location where a second communications protocol operates to adestination, the centre including: a receiver for receiving the callcontrol signal and the multiplexed stream at the predetermined location;a de-multiplexing module for de-multiplexing the multiplexed streambased on a first component part in the call control signal; a decodingmodule for de-coding the remaining components based on a secondcomponent part in the call control signal; and a signal processingmodule for recombining the remaining components to enable monitoring tothe original multimedia call.

There are a number of advantages provided by the various aspects of thepresent invention. One advantage is that the invention allows compliancewith the existing lawful interception requirements by means of asimplified implementation which reduces the amount of informationtransmitted from one node to another. This is achieved by removing thecontrol signaling and multiplexing the video and audio components into amultiplexed stream. The method and apparatus ensures that the mediagateway control function (MGCF) logical functions can be combined witheither the Mobile Switch Centre (MSC) or Gateway MSC (GMSC). The methodand apparatus also allows legal interception to be carried out for MMTelcalls using a CS node. Any changes made during the call to either thecodec or multiplexing schemes can also be taken into consideration.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings, in which:

FIG. 1 is a block diagram of the lawful intercept management system inaccordance with 3GPP technology standards;

FIG. 2 is a block diagram for illustrating monitoring of a video call,in accordance with an embodiment of the invention, by way of example;and

FIG. 3 is a flow chart for illustrating the method steps for monitoringa video call, in accordance with an embodiment of the invention, by wayof example.

DETAILED DESCRIPTION

A CS video call consists of three main components. The first is a videochannel characterized by the video codec. The second is an audio channelcharacterized by an audio codec. The third is the control channel (inaccordance with the H.245 protocol) that provides control information inrelation to the terminal capabilities and the opening and closing ofchannels. In addition, the control information defines the multiplexingscheme which is applied to multiplex the CS video call components into asingle 64 kb per second UDI (Unrestricted Digital Information) CS databearer.

If a video call takes place purely in the CS domain the existing priorart solutions for monitoring calls for lawful interception are perfectlyadequate. However, as the increase in the Internet protocol “network”continues it is much more likely that the call, for example, willcommence in the CS domain move into the IMS domain and then maybe backinto the CS domain for termination. Any time a video call crosses overfrom one domain to another the present invention will provide thesolution to dealing with the problem of lawful interception of callsthat change domain. The example presented is in respect of the CS domainand the IMS domain; however, it will be appreciated that othercommunication protocols may make use of the same principles as thepresent invention, although they may be adapted from case to case.

In any interworking situation the signals that arrive at, for example, aGateway Mobile Switching Centre (GMSC) where call forwarding istriggered in the GMSC, are from one protocol and are handled as if theywere from another protocol. For example, the GMSC may receive anincoming Session initiation protocol (SIP) video call from the IMSdomain which includes two real-time transport protocol (RTP) streams,one for video and one for audio, but may handle the call according tothe CS data principles applicable to CS data calls. Clearly, this is notgoing to enable lawful interception of the SIP video call because thereis no knowledge of the coding or multiplexing of the constituentsignals.

Interworking is similarly a problem with Multimedia Telephony (MMtel)calls from one network or terminal to another via an IMS interface foreach network or terminal, with traffic passing through the CS domain.Routing all MMtel calls through the CS domain to allow for lawfulinception will work for speech calls, but will not work for video orother sorts of multimedia calls.

Lawful interception in the CS domain still requires the video content isin the 64 kb per second UDI format. However, the RTP streams of videoand audio do not comply with this. In addition, the H.245 controlsignaling is not received at either side of the CS node and would berequired at the monitoring centre in order to decode any possible UDIstream. In order to do this the control information would need to begenerated in the CS node for any incoming video call just in case thecall may require lawful interception at a later date. This would impactthe capacity of the node and may result in a costly implementation. Oneof the most important requirements of lawful interception is that theinterception process is not allowed to add information to the datastreams. So adding the control signaling that is sent to the monitoringcentre by the CS node would break an essential legal requirement.

The defined requirements for lawful interception are shown in FIG. 1. Alawful interception management system (LI-IMS) 100 is connected to a lawenforcement monitoring facility (LEMF) 102. A CS node 104 connected to amedia gateway (MGW) 106 communicates with the LI-IMS. The communicationbetween the CS node and the LI-IMS is in the form of a first set ofsignals relating to administration and alarm 108 and a secondcommunication 110 relating to interception of related data. In turn theLI-IMS sends to the LEMF a first set of signals relating toadministration and alarm 112 (this is often called the HI1 signal) and asecond communication 114 (this is often called the HI2 signal) relatingto interception of related data. If required the LEMF can obtain thecontent of a particular communication from the MGW 106 via route 116(this is often called the HI3 signal). HI stands for handover interfacein each of the above three examples.

As previously indicated above, for video or other multimedia calls thatdo not provide H.245 control signaling lawful interception from the CSnode is not possible. However, the present invention provides thesolution by multiplexing the audio and video RTP streams into a singleUDI stream that does not include any control signaling. The controlsignaling, i.e. the information concerning the multiplexing scheme andcodecs used in a monitored video call, are provided as additionalinformation sent to the monitoring centre in a specific manner. Forexample the additional information may be sent as a printout that isfaxed; communicated by computer means or in any other appropriatemanner. The monitoring centre can then use the additional information todecode recorded call content at a later time. The additional informationincludes details of the multiplexing scheme, audio codec information andvideo codec information used for that call.

The method will now be described in greater detail with reference toFIG. 2. In accordance with lawful interception rules, the lawfulinterception process is not allowed to add any information to any callwhich is intercepted. The process of multiplexing does not addinformation to the call nor does it alter the call in any way. Referringto FIG. 2 a video call is made between. The call set up includes theexchange of SIP (session initiation protocol) signals and SDP (SessionDescription Protocol) information for media description between CS node204 on hand and IMS 200 respectively IMS 202 on the other hand. The callis passed through CS node 204 and media gateway (MGW) 206. The MGWgenerates the data for lawful interception which is sent to the LImonitoring centre 208. The audio and video RTP streams from theoriginating side of the video call (IMS 200) are multiplexed into asingle UDI stream 210 and forwarded to the monitoring centre. The CSnode data, which includes details of the multiplexing scheme, audiocodec information and video codec information used for that call, andwhich may be extracted from received SDP information or extracted in anyother way, may be transmitted to the monitoring centre in a separatecommunication 212. As previously indicated the separate communication212 may be made by any appropriate means.

Similarly, the video and audio RTP streams received from the terminatingside of the video call (IMS 202) are multiplexed into another UDI stream214 which is also forwarded to the monitoring centre. The CS nodegenerates two CS UDI calls (216 and 218) towards the monitoring centreone for each direction. This operates using either BICC or ISUPsignaling.

It should be noted that splitting the call into audio and video streams(which are then multiplexed) and a set of control signals may be usedfor the call between the originating and terminating side of the call aswell as in any communications with the LI monitoring center. This has anumber of advantages, as it can effectively reduce the bandwidthoccupied by the component video call.

Whatever the destination of the multiplexed audio and video streams,they cannot be decoded without knowledge of what multiplexing scheme wasapplied and what codecs were used for the original audio and videocoding. Accordingly, at the terminating end of the call or at theLI-monitoring centre it is necessary to know the following information:

-   -   the audio codec;    -   the video codec; and    -   the manner in which the audio and video are multiplexed into        information units (i.e. whether these are singular or spread        over multiple multiplexed information units).        The combined information (the call control signal) mentioned        above constitutes part of the content of the multimedia call, in        this case a video call. It will be appreciated that for other        types of multimedia call the call control signal and the other        content of the call may comprise different elements, depending        on the nature of the multimedia call.

The control information must be provided in addition to the UDI datastreams containing video and audio. There are a number of options as tohow the codec information can be communicated. The first option is inaccordance with FIG. 2, where the information is added to the ISUP/BICCcontrol signaling and communicated therewith. This will require changesto the ISUP/BICC protocol to be effective. In addition as the video andaudio codecs may change during the ongoing video call the informationwill need to be updated if any changes to the codec occur.

In a second option the information required to decode the audio andvideo UDI stream is communicated by other means. For example, at videocall setup a data printout is sent to the monitoring centre to identifythe multiplexing and coding schemes used to the call. This may be in theform of a list; a database entry or identifier; or whatever whichidentifies the call, the time of the call, the codecs used etc. Theinterface for providing this information, is already defined and used in3GPP under the name HI2 as indicated above. If there are any changes ofthe codec for the video or audio during the duration of the call anotherprintout is sent to the monitoring centre at the time of the call. Thesecond printout contains, at least, the new codec type and a timestampindicating the point in time at which the change was made.

In relation to the communication of the multiplexing scheme there arealso a number of options. A first option is that the multiplexing schemeis simply added to the data printout sent to the monitoring centre. Ifthere are any changes to the multiplexing scheme during the duration ofthe call the second printout is generated for transmission to themonitoring centre.

A second option requires that the multiplexing schemes are predefined byagreement between the network operator and the authorities running themonitoring centre. This agreement would define the multiplexing schemefor each audio and video codec type and any combination thereof.

The combination of options used for determining and transmitting theinformation relating to coding and multiplexing will depend on whetherthe call is going to a call destination or to a lawful interceptionmonitoring centre. In either case where real-time de-multiplexing anddecoding are required the options that provide control signalingdirectly to a destination will be the preferred options. In themonitoring centre however, it is not always necessary to decode andde-multiplex the streams either in real time of otherwise, however whendecoding and de-multiplexing are required, these may be delayed to alater time if necessary. Accordingly, the monitoring centre stores theentire contents of the call (i.e. the full stream received from bothsides of the call). If and when the call needs to be the multiplexed ordecoded, the additional data received from the CS node is correlatedwith the recorded streams to first de-multiplex the streams into theoriginal coded audio and video streams. Then once the video and audiostreams have been identified, those can be extracted by decoding usingthe appropriate decoder. Clearly, if either multiplexing scheme orcoding scheme has changed during the call, appropriate changes will needto be made at the point of de-multiplexing and decoding the storedinformation at the monitoring centre.

There are a number of advantages to the present invention. Firstly theinvention allows compliance with the existing lawful interceptionrequirements by means of a simplified implementation which reduces theamount of information transmitted from one node to another. This isachieved by removing the control signaling and multiplexing the videoand audio components into a multiplexed stream. The method and apparatusensures that the media gateway control function (MGCF) logical functionscan be combined with either the Mobile Switching Centre (MSC) or GatewayMSC (GMSC). The method and apparatus also allows legal interception tobe carried out for MMTel calls using a CS node. Any changes made duringthe call to either the codec or multiplexing schemes can be taken intoconsideration.

In the present invention a multiplex of audio and video signals isformed and the control information is extracted in order to reduce theload and provide a manageable stream which can be stored using lessmemory capacity. In addition, where appropriate the invention provides areal-time means to transmit the information relating to the video call.The multiplex of audio and video signals without control information, isof a lower bandwidth than the video call were it not multiplexed orwithout control information. This clearly has a number of advantages.Similarly, providing information for de-multiplexing and decoding theRTP received stream requires a number of solutions to problems, as havebeen presented herein.

Referring to FIG. 3, the method steps of the present invention are nowpresented. A video call is initiated at step 300. The audio and videostreams are multiplexed into a single multiplexed stream and the controlsignaling is extracted at step 302. This can take place at anyappropriate point in the transmission channel from the originating toterminating end of the video call, but is generally at a CS node in theCS domain. The multiplexed audio and video stream are then sent to thelawful interception monitoring centre or to the destination (as isrequired), step 304. In a separate process the control information orsignaling is sent to the lawful interception monitoring centre or thedestination in step 306. At a certain point in time in the future(real-time for the destination and any time for the lawful interceptionmonitoring centre) the audio and video components are de-multiplexed anddecoded (step 308) based on the control information or signaling sent atstep 306. At step 310 and video call can be viewed and heard either atthe lawful interception monitoring centre or the destination (as thecase may be).

In order to carry out the method steps identified in FIG. 3 a number ofmodules for carrying out the steps may be found in for example the CSnode and the MGW in FIG. 2. The modules include a multiplexing modulefor multiplexing the audio and video streams prior to them beingtransmitted to the lawful interception monitoring centre. In addition,signal processing module for removing and processing the call controlsignals in order for them to be communicated to the lawful interceptionmonitoring centre is also provided. At the lawful interceptionmonitoring centre there are equivalent modules for receiving,de-multiplexing, decoding and processing the received signals and alsofor storing the call control signals and the multiplexed stream untilsuch time as the signals need to be decoded (if ever).

In the embodiments described above, the emphasis has been on identifyingthe coding and multiplexing schemes of a particular multimedia call inorder to enable the lawful interception to de-multiplex and decode thecall. However, it will be appreciated, that other call parameters may becaptured as the control information relating to the multimedia call toenable identification of the content of the multimedia call for thepurposes of lawful interception.

It will be appreciated there are many alternatives to the embodimentsdescribed above, which would still fall within the spirit and scope ofthe present invention.

1. A method of facilitating monitoring of a multimedia call made up of aplurality of component parts, to enable the multimedia call contents tobe identified at a predetermined location, the multimedia calloriginating from a location at which a first communications protocoloperates and passing through at least one location where a secondcommunications protocol operates to a destination, the method comprisingthe steps of: identifying the component parts of the multimedia call;extracting one or more control signals from the component parts to forma call control signal for the multimedia call and a set of remainingcomponent parts of the multimedia call; forming a multiplexed stream ofthe remaining component parts of the multimedia call; independentlytransmitting the call control signal and the multiplexed stream to thepredetermined location to enable the component parts of the multimediacall to be determined in order to identify multimedia call contents. 2.A method as claimed in claim 1, wherein the step of independentlytransmitting the call control signal and the multiplexed streamcomprises transmitting the call control signals in a first type ofcommunication.
 3. A method as claimed in claim 2, further comprisingtransmitting the call control signal as a printout communicated to thepredetermined location as the multimedia call is set up.
 4. A method asclaimed in any preceding claim, wherein the step of independentlytransmitting the call control signals and the multiplexed streamcomprises transmitting the multiplexed stream in a second type ofcommunication.
 5. A method as claimed in any preceding claim, furthercomprising transmitting the multiplexed stream as a single UDI(Unrestricted Digital Information protocol) signal.
 6. A method asclaimed in any preceding claim, further comprising originating inmultimedia call from an IP multimedia subsystem (IMS) network.
 7. Amethod as claimed in any preceding claim, further comprising passing themultimedia call through at least one location where a circuit switched(CS) protocol operates.
 8. A method as claimed in any preceding claim,further comprising providing information from a lists consisting of: amultiplexing scheme, a coding scheme, or call parameters, as the callscontrol signal.
 9. A method as claimed in any preceding claim, furthercomprising transmitting the call control signal and the multiplexedstream to a lawful interception monitoring centre.
 10. A module for acommunication network for facilitating monitoring of a multimedia callmade up of a plurality of component parts, to enable the multimedia callcontents to be identified at a predetermined location, the multimediacall originating from a location at which a first communicationsprotocol operates and passing through at least one location where asecond communications protocol operates to a destination, the modulecomprising: a signal processing module for extracting one or morecontrol signals from the component parts to form a call control signalfor the multimedia call and a set of remaining component parts of themultimedia call; a multiplexed module for forming a multiplexed streamfrom the remaining component parts of the multimedia call; independenttransmission modules for transmitting each of the call control signaland the multiplexed stream to the predetermined location to enable thecomponent parts of the multimedia call to be determined in order toidentify multimedia call contents.
 11. A module as claimed in claim 10,wherein the call control signals form a first type of communication. 12.A module as claimed in claim 11, wherein the first type of communicationis a printout communicated to the predetermined location as themultimedia call is set up.
 13. A module as claimed in any of claims 10to 12, wherein the multiplexed stream forms a second type ofcommunication.
 14. A module as claimed in any of claims 10 to 13,wherein the multiplexed stream forms a single UDI (Unrestricted DigitalInformation protocol) signal.
 15. A module as claimed in any of claims10 to 14, wherein the multimedia call originates from an IP multimediasubsystem (IMS) network.
 16. A module as claimed in any of claims 10 to15, wherein the multimedia call passes through at least one locationwhere a circuit switched (CS) protocol operates.
 17. A module as claimedin any of claims 10 to 16, further comprising including information froma lists consisting of: a multiplexing scheme, a coding scheme, or callparameters, as the calls control signal.
 18. A module as claimed in anyof claims 10 to 17, further comprising transmitting the call controlsignal and the multiplexed stream to a lawful interception monitoringcentre.
 19. A computer program comprising instructions for carrying outthe method according to any of claims 1 to 9, when said computer programis executed on a computer system.
 20. A method of monitoring, at apredetermined location, a multimedia call made up of a plurality ofcomponent parts which plurality of components have been separated into acall control signal and a multiplexed stream made up of a multiplex ofremaining components which do not form part of the call control signal,the multimedia call originating from a location at which a firstcommunications protocol operates and passing through at least onelocation where a second communications protocol operates to adestination, the method comprising the steps of: receiving the callcontrol signal and the multiplexed stream at the predetermined location;de-multiplexing the multiplexed stream based on a first component partin the call control signal; de-coding the remaining components based ona second component part in the call control signal; recombining theremaining components to enable monitoring to the original multimediacall.
 21. A lawful interception monitoring centre for monitoring amultimedia call made up of a plurality of component parts whichplurality of components have been separated into a call control signaland a multiplexed stream made up of a multiplex of remaining componentswhich do not form part of the call control signal, the multimedia calloriginating from a location at which a first communications protocoloperates and passing through at least one location where a secondcommunications protocol operates to a destination, the centre including:a receiver for receiving the call control signal and the multiplexedstream at the predetermined location; a de-multiplexing module forde-multiplexing the multiplexed stream based on a first component partin the call control signal; a decoding module for de-coding theremaining components based on a second component part in the callcontrol signal; a signal processing module for recombining the remainingcomponents to enable monitoring to the original multimedia call.